1. Field of the Invention
This invention belongs to the field of fatty carboxylic acids and their esters and, more particularly, to the field of processes for reducing the polyunsaturates content of fatty acids and/or fatty acid esters.
2. Description of the Prior Art
Processes for preparing dimeric fatty acids are known. U.S. Pat. No. 2,731,481 to Harrison, et al. describes the dimerization of monounsaturated fatty acids, such as oleic acid, to provide dimeric acids which retain the unsaturation of the fatty acids from which they are prepared. To accomplish this, higher fatty acids or esters thereof having only one double bond in the fatty group are heated in an inert atmosphere to temperatures in excess of 50.degree. C. in the presence of an organic peroxide catalyst of the formula ROOR.sup.1, in which R is a tertiary alkyl group and R.sup.1 is selected from the group consisting of tertiary alkyl and tertiary alkyl peroxyalkyl groups, e.g. di-tertiary butyl peroxide.
In accordance with the dimerization process described in U.S. Pat. No. 2,964,545, conjugated diunsaturated fatty acids or their lower alkyl esters, alone or in admixture with other fatty acids, either saturated or unsaturated, are converted to dimeric fatty acid under substantially the same conditions and in the presence of the same or similar organic peroxides disclosed in U.S. Pat. No. 2,731,481 to Harrison, et al., supra. Given the teachings of U.S. Pat. No. 2,731,481 to Harrison, et al. that monounsaturated fatty acids will undergo dimerization under essentially the same conditions which U.S. Pat. No. 2,964,545 to Harrison teaches will result in the dimerization of conjugated diunsaturated fatty acids, one skilled in the art would not consider the selective peroxide-initiated polymerization of diunsaturated fatty acids and/or fatty acid esters such as linoleic acid and/or methyl linoleate present in admixture with monounsatured fatty acids and/or fatty acid esters such as oleic acid and/or methyl oleate to be possible.
U.S. Pat. No. 3,950,365 to Singer, et al. describes a method for the purification of fatty acid mixtures, said to be especially useful for the production of oleic acid which is relatively free of linoleic acid, in which a fatty acid mixture is heated to 90.degree.-150.degree. C. in the presence of a particular type of organic microporous acid ion exchange resin resulting in selective dimerization/trimerization of the polyunsaturated fatty acid components of the mixture (e.g., linoleic acid) greatly increasing the boiling points of the polyunsaturates and facilitating their removal by distillation. There is no suggestion in this patent of selectively polymerizing polyunsaturated fatty acids in a fatty acid mixture employing a peroxygen compound. As noted above, one skilled in the art would have no reason to expect such a selective polymerization to be possible since the Harrison, et al. and Harrison patents show that both oleic acid and linoleic acid undergo dimerization when treated with peroxide.